1. Technical Field
The present invention relates to an optical recording device and an optical recording and reproduction device.
2. Related Art
Recently, as a holographic memory recording and reproduction method, there has been proposed the coaxial recording method (collinear method) that has advantages in that its optical system can be significantly simplified in comparison to the conventional two-beam interference method, it is resistant to external disturbance such as vibration, and the introduction of a servo mechanism is easy. In this collinear method, signal light and reference light that have been modulated and generated by a spatial light modulator are collected with the same optical axis by the same lens, and an interference fringe (diffraction grating) that is formed by the interference between the signal light and the reference light is recorded as a hologram on an optical recording medium. A signal light pattern in which digital data have been two-dimensionally encoded is displayed on the spatial light modulator, whereby the digital data are superposed on the signal light.
The optical recording medium on which the hologram has been recorded is irradiated with the reference light as reading light, whereby the signal light is reproduced from the recorded hologram. From this reproduced signal light, the superposed digital data can be decoded. However, in the conventional collinear method, since the signal light and the reference light are on the same optical axis, when the optical recording medium is irradiated with the reference light as reading light during reproduction, light leaking to the region of the spatial light modulator that corresponds to the signal light. For example, when the precision of liquid crystal elements that have been disposed as a transmissive spatial light modulator is low, the light that has been transmitted through the OFF pixels that are in display positions of the signal light pattern becomes leak light. Consequently, when all of the pixels of the spatial light modulator are irradiated with light in this manner, this leak light is detected by a photodetector, noise with respect to the reproduced signal light is generated, and reproduction characteristics deteriorate.